The present invention relates to a room temperature-curable organopolysiloxane composition, more particularly, to a room temperature-curable organopolysiloxane compostion suitable for use as a material for imprinting or blocking of form which lacks problem of retardation of curing rate or incomplete curing, even after prolonged storage at an elevated temperature.
Among various types of room temperature-curable organopolysiloxane compositions known in the prior art, those used as a material for imprinting or blocking of form are mainly of the type in which curing of the composition proceeds by the addition reaction between an organopolysiloxane having vinyl groups bonded to the silicon atoms and an organohydrogenpolysiloxane having hydrogen atoms directly bonded to the silicon atoms in the presence of a platinum compound as a catalyst.
The room temperature-curable organopolysiloxane composition of the above mentioned type is usually supplied in two packages each of which has a different content and is storable with stability from the other and the contents of the two packages are mixed together directly before use to complete a curable composition. For example, the content of one of the two packages contains the organopolysiloxane having vinyl groups while the content of the other package contains the organohydrogenpolysiloxane. It is a usual formulation with an object to facilitate mixing and handling of the composition by reducing stickiness of the composition under mixing on to the mixing tools and handling fingers that either one or both of the contents are admixed with an internal releasing agent which may be typically an aliphatic hydrocarbon compound having a consistency of a liquid or semi-solid at room temperature such as liquid paraffins and petrolatums.
A problem in such a formulation having an aliphatic hydrocarbon compound as an internal releasing agent in the composition is that the additive compound is susceptible to catalyic oxidation in the presence of a platinum compound as the catalyst for the addition reaction or by the activity of certain active groups on the surface of the inorganic filler particles conventionally added to the composition to produce various oxidized compounds such as carboxylic acids, aldehydes, hydroperoxides and the like which in turn may at least partially deactivate the platinum catalyst so as to cause problems such as curing retardation or incomplete curing when the room temperature-curable organopolysiloxane composition is to be cured.
Retardation in curing rate is a particularly serious problem when the room temperature-curable organopolysiloxane composition is used as a material for imprinting or blocking in dental or medical applications such as preparation of a mold for artificial teeth or for an insert in an external auditory canal because, while, in such an application, the curable composition prepared by uniformly mixing the contents of the two packages taking 20 to 60 seconds and applied to the part of the human body is required to be fully cured within, for example, 3 to 5 minutes before the cured composition is removed from the body. The patient under treatment, who is compelled to remain motionless until full curing of the composition, is subjected to excessive pain by the retardation in curing rate.
In view of the sometimes lengthy marketing route of the products of this kind, which not infrequently exceeds a half year to two years before the product is received by a consumer, a formulation of the room temperature-curable organopolysiloxane composition of this type which is free from the problem of curing retardation or incomplete curing even after prolonged storage is much desired since otherwise the product must be stored at low temperatures or in a hermetically sealed container filled with an inert gas such as nitrogen, which causes great inconveniences and economical disadvantages.